生物合成基钻井液在长宁页岩气水平井的应用

油基钻井液的抑制性、封堵性强，润滑性好，对水敏感的泥页岩地层有极强的防塌作用，是四川长宁页岩气井水平段采用的主要钻井液体系，但油基钻屑因含有石油烃类、重金属和有机物等污染物，若直接排放，会对周边生态环境造成严重危害，加之目前含油岩屑的处理能力不足，导致环境保护压力巨大，油基钻井液综合成本过高，因此其使用受到一定限制。长宁CN-H井是部署在四川省宜宾市珙县的一口页岩气水平井开发井，钻探目的层为长宁下古生界龙马溪页岩层。该井四开井段泥页岩地层易水化分散、易垮塌，井壁失稳风险大，使用了一种生物合成基环保钻井液钻井，取得了良好的效果。该生物合成基钻井液流变性优异，具有良好的润滑性、封堵性、抑制性，且热稳定性好，高温下仍具有较强的悬浮和携带岩屑能力，在水平段钻进中实现了高效安全钻进。该生物合成基钻井液无毒无害，满足安全环保要求。 

Application of a Biosynthetic Base Drilling Fluid in Shale Gas Drilling in Block Changning

The well CN-H in the Block Changning is a shale gas development horizontal well located in Gong County, Yibin City, Sichuan. The target zone of this well is the Longmaxi shale formation of the lower Palaeozoic group. Shale formations in the fourth interval of the well is easy to hydrate and disperse, and collapse, causing borehole instability during drilling. Oil base drilling fluids are not allowed to use in drilling operations because of environment protection requirement. A biosynthetic base drilling fluid was then developed to replace oil base drilling fluids. The continuous phase of the biosynthetic base drilling fluid is a vegetable oil modified with a special technique. The biosynthetic base drilling fluid functions normally at 200℃, and the density of the drilling fluid is adjustable between 1.10 g/cm3 and 2.50 g/cm3. A biosynthetic base mud formulation of 2.1 g/cm3 had a rate of linear expansion of 0.8% and extreme pressure friction coefficient of 0.089 after aging at 150℃. The HTHP filtration rate of the aged mud was 1.6 mL. These data indicated that the synthetic base drilling fluid has good lubricity, plugging capacity, and inhibitive capacity, as well as good high temperature stability. Good suspension performance and cuttings carrying capacity of the drilling fluid at elevated temperatures ensured efficient and safe drilling in horizontal section of the well. Borehole wall was satisfactorily stabilized in drilling the fourth interval of the well CN-H. Average percent hole enlargement of this well was 4.9%, and the average ROP was 9.74 m/h, 2.14 m/h higher than those wells drilled with oil base drilling fluids. The biosynthetic base drilling fluid is nontoxic, satisfying the requirements of environment protection in Changning.